Most bonding systems that contain carboxylated monomers for priming and hydrophilic monomers for bonding require a number of consecutive procedural steps after conditioning with an acid which are aimed at optimizing the adhesion to dentin. These include (1) mixing of a primer monomer with a co-monomer/co-initiator, usually a secondary or tertiary aromatic amine, e.g. mono- or bivalent salts of bis-(N-tolyl glycine glycidyl methacrylate) and (2) priming of the prepared dentin surface with this mixture(Bowen, 1985; Bowen, 1986; Bowen, 1987; Venz and Dickens, 1991; Venz and Dickens, 1993; Bowen, 1993; Bowen, 1994; Ibsen et al., 1994; Suh et al., 1994). The third step comprises application of an unfilled bonding resin, which will then be light-cured. The bonding resin consists mainly of 2,2-bis[p(2'-hydroxy-3'-methacryloxypropoxy)phenylene]-propane (bis-GMA) and 2-hydroxyethyl methacrylate (2-HEMA).
A different approach was taken by Waknine (1992) who disclosed a three-step adhesive system that contains a nonacidic carbonate monomer instead of the carboxylated resin and a different type of amine accelerator. The bond strengths reported by Waknine are on the order of about 10 MPa.
Recently, abstracts describing bonding to dentin with one-component (better described as one-solution) adhesive resin systems have been reported (Jia et al., 1996; Kelsey et al., 1996; Latta et al., 1996; Qian et al., 1996; Dickens et al., 1997). More recently, a patent (Qian et al., August 1997, U.S. Pat. No. 5,658,963) has been issued describing one-step formulations. These adhesive resin formulations comprise in a single solution the components that were applied in the multistep system in several sequential steps as described above. The components are: the bonding resin consisting of a viscous monomer, bis-GMA, and the diluent monomer 2-HEMA, as well as light-sensitive polymerization catalysts, an amine accelerator, and acetone and/or ethanol as the solvent(s).
Various U.S. patents disclose use of other one-solution systems. Bunker and Fields, (1985); Aasen, (1988); Bunker, (1994) describe polymerizable phosphate esters. However, these bonding systems yielded a relatively low bond strength to dentin of about 9 MPa Also, these bonding systems contain a multitude of polymerizable components in their systems, among which are phosphate esters. These esters can hydrolyze, thus releasing free acid, which can, in turn, lead to hydrolysis of methacrylate esters resulting in the release of methacrylic acid and loss of the polymerizable functionality on the resin Thus, phosphate esters are less stable than the carboxylic acid esters described in this invention. Bunker et al (1985), reported mixing the adhesive with a solution of sodium benzene sulfinate as a coinitiator, which adds another step to these so-called one-step formulations.
James (1987) describes adhesive compositions for tooth enamel, but does not teach adhesion to dentin.
Blackwell and Huang (1987, 1989) and Huang and Blackwell (1990) describe phosphate esters of mono- or dipentaerythritol. However, use of the experimental formulations reported by Blackwell and Huang (1987, 1989) resulted in relatively low bond strengths to dentin (about 8.4 MPa). Higher bond strengths were reported by Huang and Blackwell (1990) but only if an unfilled bonding resin was applied as a second step after priming Also, the storage stability of these phosphate-containing resins was less than desirable, possibly due to the above described hydrolysis of the ester group.
There is a need in the art for new methods and compositions for adhesives for use in restoring teeth in which the bond strength is good, the steps and reagents are kept to a minimum, and the time required for the restoration is short.